Certain objects, such as plastics and metals, can be manufactured using a mold. For example, an object may be manufactured by injection molding. A mold is first created. Materials, typically in a substantially liquid and raised temperature form, are injected into the mold. When the materials are cooled and return to a solid form, the object may be removed from the mold.
Each mold typically includes multiple sections. The sections are designed to be able to removably mate with each other. Further, the molded object may be removed or “pulled away” from one or more of the mold sections. The direction in which each mold section is pulled away from the molded object is referred to as the “pull direction”.
FIG. 1A illustrates a simple sphere 110 and a mold section 120 of a mold employed in the creation of the sphere 110. FIG. 1B illustrates an expanded view of a portion 140 of the mold/sphere interface. The draft angle 150 is defined as the smaller angle between the surface of the sphere (more specifically the tangent 160 to the sphere) and the pull direction 130. Further, typically, the reference coordinate system is “positioned” such that large positive values of the draft angles 150 denote relative ease in “pulling” the mold 120 away from the object 110, draft angle values around 0 denote relative difficulty in “pulling” the mold 120 away from the object 110, and large negative draft values denote virtual “impossibility” in “pulling” the mold 120 away from the object 110. In fact, in the last case, the object 110 may be “pushed” into the mold 120, as opposed to being “pulled” from the mold 120. Thus, information about the draft angles of a pull direction at various locations of a molded object is useful to a designer.